Adidas 1 and Nike Free 5.0, two newfangled sneaker concepts, could hardly be more dissimilar. With a motor implanted below the arch, adidas 1 constantly tightens and loosens itself to create a custom fit. A company official, with a straight face, calls it the "world's first intelligent shoe." It may also be the world's first $250 sneaker.

Nike Free, at the slightly more bearable price of $80, is built around an ultra-flexible sole, scored deeply from heel to toe, to mimic barefoot walking or running. Why pay for what is, essentially, an anti-shoe? Because navigating in it strengthens the foot, of course. "It's a weight room for your feet," says Nike engineer Tobie Hatfield.

Amid the fevered back-to-school shopping binge, the top shoemakers are talking, perhaps more than ever, about technology.

Pumps (yes, they're back). Sensors. Shocks. (Or Shox, as Nike calls them.) Or ClimaCool, which Adidas says channels air through the sneaker to cool the foot.

The sci-fi-sounding bells and whistles are fueling a $15 billion athletic footwear industry that cranks out a shoe for every activity, sport, season and lifestyle. Reebok's Zan Chi Yoga/Pilates slip-ons, for example, help you "find your inner 'chi,' " according to the company.

In case you missed the cultural memo, the age of the all-purpose sneaker is over.

In 2004, consumers spent $237 million just on aerobic shoes (lightweight materials to prevent foot fatigue), $234 million on skateboarding shoes (thin soles to control the board) and $43 million on cheerleading shoes (finger notches to be grabbed during stunts), according to National Sporting Goods Association. Then there are the big categories: $3.5 billion on walking shoes (rigid fronts to protect toes), $1.9 billion on running shoes (thick soles to absorb impact) and $877 million on basketball shoes (high-tops to prevent ankle injuries).

"When manufacturers come out with a new shoe, technology is where they begin," says Dan Kasen, manager of information services at the National Sporting Goods Association. "It is a critical consideration."

Nike has put its marketing muscle behind the Free. The sneaker has its own Web site, whose introduction seems to suggest the Free will turn a pickup game of basketball or a run around the track into a back-to-Eden, barefoot experience. "In the beginning there was the foot. And that was good. That's why we designed a shoe that lets the foot run free. On any surface."

Adidas 1 has its own Web site, too. The company says the shoe, introduced first for runners, helps customize footwear in a world where body weights and foot shapes can vary widely. Two people might buy the same running shoe — size 9, perhaps — but one weighs 120 pounds, and the other 200. "Before now, you could never change cushioning," says Christian DiBenedetto, who helped develop the adidas 1.

Now you can. A cable, attached to the sneaker's cushioning and running underneath the arch, works with a microprocessor and electric motor to adjust the fit with every step. (A battery must be periodically replaced.) Adidas 1's value for the non-runner is less clear. "Is it going to do them any harm? Absolutely not," DiBenedetto says.

Reebok has resuscitated the pump, but this time there is no need to squeeze the tongue of the shoe. With the Pump 2.0, an air-filled chamber automatically takes on the contour of the foot after five to 10 steps. (The pump places enough pressure against the foot that laces are unnecessary.) Another version, called the Pump Wrapshear, lets buyers turn off the pump, should they tire of all that customization.

Donald Wilson, a competitive runner, owns 30 pairs of sneakers — a few Nikes, a few adidas, a few Pumas — each with its own function. Some are for running 5K races, others for marathons. One pair is designated for running on trails; another for running on concrete.

But his rule of thumb: When a sneaker costs more than $100 "you are usually looking at too many bells and whistles."

Stephen M. Pribut, a podiatrist and president of the American Academy of Podiatric Sports Medicine, has even simpler advice for sneaker buying: "If you've never had a problem with your feet, don't change."

Adidas 1: Called "world's first intelligent shoe."

Reebok's Pump Wrapshear: The pump is back, but this one lets you shut it off if you want to.